In Isle Royale National Park (Michigan), there is an established population of both gray wolves and moose.  It is believed that the wolves arrived on Isle Royale sometime during the 1940s when an ice bridge formed, allowing for wolves to cross over the water to the island.  Ever since the wolves arrived, they have been an important predator on the island, helping to control the local moose population.  The wolves do this by preying on ill or injured moose.  Recently, the wolves have faced the threat of extinction in Isle Royale National Park due to inbreeding (National Park Service, 2022).

There have been fluctuations in the wolf and moose populations in Isle Royale for many years. Some factors include the available amount of food resources and weather changes.  However, a common pattern that has been seen is that when the wolf populations spike, the moose populations decrease and vice versa.  This can be seen in the following graph below.  From 2011 to 2014, the wolves had reached a population size that was unsustainable.  Around 2011, the wolf population decreased, and the moose population increased. (National Park Service, 2021).

(National Park Service, 2021)

If there is low genetic variation within a population, then a species risks extinction, therefore lowering its fitness.  The wolves on Isle Royale are facing this problem, likely due to climate change not allowing for the ice bridges to form anymore.  With no ice bridges forming, the amount of gene flow that occurs in the populations has decreased.  For example, in 1997, a wolf known as M93 crossed the ice bridge to Isle Royale, creating gene flow within the population.  By 2008, 59.4 % of the wolf population descended from wolf M93.  Once this ice bridge was no longer forming, the gene flow in the population decreased, causing increases in inbreeding.  By 2012, there were only 9 wolves left, and 5 of them, through genetic testing, were found to be full siblings (Hedrick, 2014).

To save the wolf populations, a technique that can be used is called genetic rescue.  Genetic rescue allows members from outside the struggling population to be introduced either naturally or by humans to add more genetic variation into the population (Hedrick, 2014).  In June 2018, the National Park Service decided to do this to help control the moose populations.  If the wolves are not present on Isle Royale, the moose population will negatively impact the island’s vegetation.  The plan is for the National Park Service to introduce a total of 20 to 30 wolves onto the island (National Park Service, 2018).

Citations

Hedrick PW, Peterson RO, Vucetich LM, Adams JR, Vucetich JA et al. (2014) Genetic rescue in Isle Royale wolves: genetic analysis and the collapse of the population. Conservation Genetics 15: 1111–1121. https://link.springer.com/article/10.1007/s10592-014-0604-1

National Park Service. 2018 Press Release National Park Service Releases Record of Decision to Introduce Wolves at Isle Royale National Park. Version 2018.6. https://www.nps.gov/isro/learn/news/press-release-national-park-service-releases-record-of-decision-to-introduce-wolves-at-isle-royale-national-park.htm. (date last accessed 12 February 2024).

National Park Service. 2021 Wolf & Moose Populations. Version 2021.5. https://www.nps.gov/isro/learn/nature/wolf-moose-populations.htm.  (date last accessed 12 February 2024).

National Park Service. 2022 Wolves. Version 2022.1. https://www.nps.gov/isro/learn/nature/wolves.htm.  (date last accessed 12 February 2024).